The invention relates to the field of integrated circuits, and more particular to the implementation of a vanishingly small area diode in an integrated circuit.
Diodes are used in a wide variety of integrated circuit applications. One such application is a circuit element that blocks the flow of current in a particular direction. In another application, the diode can be used as a voltage clamp or to provide a reference voltage. Diodes are used to provide electrostatic discharge circuit protection for integrated circuit elements that are particular susceptible to electrostatic damage. In some fast switching integrated circuit applications, diodes with very short switching times are used.
Integrated circuit diodes are typically made by defining a window in a thick field oxide and implanting or diffusing a dopant species such as arsenic, phosphorous, or boron. This results in the formation of a p-n junction diode with an area defined by the capability of the photolithography used to define the window. In addition to photolithography, the implant depth and the amount of diffusion of the species will also determine the size of the diode.
Along with the increasing complexity of integrated circuits there is a corresponding increase in the packing density of the devices making up the circuit. One of the main constraints on the packing density of integrated circuits is the area that each device occupies.
In complex integrated circuit applications diodes with very short switching times are often required. Typically this is accomplished by implanting or diffusing a species which will act to reduce the carrier lifetime in the active diode region. This additional implant and diffusion adds complexity and cost to the process.
Programmable array structures are essential in applications in which there is a need for the circuit to be configured by the end user. This requires a method of forming the structure and/or defining the electrical connections after the processing of the integrated circuit has been completed. Such a structure often requires complex metallization patterns and fusable links.
Accordingly, it would be desirable to implement a very small area programmable diode with a fast switching time without an increase in process complexity or cost.
The instant invention involves the implementation of a vanishingly small diode with a very short switching time without adding process complexity and cost. In addition, it provides a method for implementing a programmable array diode structure.
An embodiment of the instant invention is a method of forming a vanishingly small diode with short switching times. The method comprises forming an area of a thin dielectric film over a conductive silicon surface of one conductivity type. This thin dielectric area is formed in a region of a thick dielectric film over the conductive silicon surface. A first conductive path is formed from the conductive silicon surface to an operating circuit. A conductive silicon film of a second conductivity type is formed over the thin dielectric region. A second conductive path is formed from the conductive silicon film to the operating circuit. A voltage is applied to the conductive silicon film which is sufficient to form at least one region of the second conductivity type in the conductive silicon surface and at least one third conductive path through the thin dielectric film. Preferably, the conductive silicon film is a polysilicon film.
Another embodiment of the instant invention is a vanishingly small integrated circuit diode with a very short switching time. The diode comprises an area of a thin dielectric film over a conductive silicon surface of one conductivity type in a region of a thick dielectric film over the conductive silicon surface. A first conductive path from the conductive silicon surface to an operating circuit. A conductive silicon film of a second conductivity type over the thin dielectric region and a second conductive path from the conductive silicon film to the operating circuit. A region of the second conductivity type in the conductive silicon surface and a third conductive path through the thin dielectric film that connects the region of the second conductivity type in the conductive silicon surface to the conductive silicon film.